JPS6037176B2 - Surface alloying and heat treatment methods - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In many industrial applications, it is desirable to produce articles whose cores are made of inexpensive, lightweight materials.

Such materials are typically non-allotropic metals including aluminum. Non-allotropic metal means a metal that has a hardness of Rc25 or less and can be hardened without undergoing transformation. The surface of such articles must also have physical properties not provided by the core material itself. Such physical properties include high hardness, high strength, high temperature wear resistance, and corrosion resistance. Some form of new surface treatment technique must be developed to obtain such properties in precisely selected surface zones without affecting the non-allotropic metal core.

That is, this cannot be achieved economically enough by applying currently known surface treatment techniques. Known processing techniques include: 'a) infiltrating the surface zone by carburizing or nitriding, {b} transforming the solidified phase of the surface zone into a harder one, (c' depositing the coating, (
d' Alloying or heat treating the entire article. Nitriding and carburizing are applicable to ferrous substrates, but not to non-ferrous materials. Transformation hardening is very effective for ferrous substrates, but not for aluminum and other non-uniform materials. The deposited coating is expensive and has insufficient durability. Processing the entire article is energy consuming, has low productivity and does not allow for the differentiation of properties between the core and surface zones. For example, in cases such as aluminum articles, the prior art primarily used precipitation hardening of the entire article.
This method is unsatisfactory for many reasons, including high cost, deformation, and low productivity. Little or no research has been conducted on surface area treatment of aluminum, and no research has been conducted on the use of highly concentrated energy beams as a factor in such surface treatment techniques. do not have. High intensity energy heat sources have been used for welding, cutting, drilling purposes, and in some cases for surface hardening of ferrous materials.

High energy beams can be used to melt very shallow surface areas of ferrous articles, allowing the molten material to transform to a harder phase when the energy beam is removed, allowing the article to act as a self-quenching medium. do. However, the technique of using high energy beams to case harden ferrous materials is completely different from that applied to non-ferrous, particularly non-ferrous materials. Little or no research has been conducted into the concept of introducing alloying elements to non-allotropic metals, such as aluminum, to controlled depths and at controlled rates through the use of high energy beams.

This lack of research is believed to be due to the existing concept that the usefulness of such beams is limited when applied to aluminum due to the following reasons: That is, 'a) materials such as these do not yield a hardened transformed phase by melting, and 'b) past experience with furnace heat treatment has shown that there is a limit to the level of hardness at which many non-allotropic metals can be hardened. 'c} No general desire for research on how to deeply harden localized zones that do not produce deformation; 'd' Alternative techniques for the general desire to harden, typically shallow, non-abrasive surfaces. For example, there is a lack of research into the effectiveness of plasma spray techniques, which do not deform the substrate and are very flexible in use. Thus, the utility of highly concentrated energy beams has not been considered for applications involving aluminum and the like. With regard to aluminum in particular, current technology may suffer from one or more of the following drawbacks.

'a} The scales of the article are highly deformed as a result of the hardening process; 'b} The surface shape of the area to be treated is irregular;
Therefore, the lack of uniform processing or the fact that the article has different cross-sectional sections and each different cross-sectional section responds differently to the hardening process, resulting in non-uniformity,'c) the cost of curing aluminum articles is expensive equipment; or relatively expensive due to the labor required; 'd' heat treatment methods cannot accurately achieve a shallow, uniform layer of hardening; {e' treatment methods provide a selective precision pattern of surface hardening over a given surface. {0 Prior art methods cannot economically cure small areas of large articles; Washing technology methods cannot cure small areas inside complex articles; h
- The prior art method cannot be used without damaging adjacent parts; 'i) The prior art method is difficult to quench; 'i) The prior art method is not suitable for very high quantities and rates of production. Not being able to adapt. Therefore, there is a need for a method for surface treatment of aluminum articles etc. that solves the above problems and improves surface treatment techniques for non-uniform materials to facilitate the achievement of all desired physical properties with proper control. exists. The main object of the invention is, in particular, to improve economy, to eliminate or reduce deformations caused by processing methods, to be suitable for articles of irregular and different cross-sectional shape, and to be suitable for articles of irregular and different cross-sectional shape, and to be suitable for the processing of the prior art. It is an object of the present invention to provide an improved method for achieving surface hardening of metal articles, which is effective for processing various metal substrates that do not require a metal article.

Another object of the present invention is to process precisely selected exposed zones of non-allotropic metal articles to provide previously unobtainable physical properties to said zones in a highly productive manner that constitutes an essentially localized casting process. The goal is to provide a way to achieve speed.

Another object of this invention is to provide a versatile method for improving the physical properties of selected surface zones of non-allotropic metals by controlled remelting in the presence of appropriate proportions of alloying constituents, which improve these properties. can be improved depending on the desired application.

Another object of the invention is to harden metals by integrating alloy-enriched surface regions of controlled width and depth. The method to achieve the above objective consists of the following requirements.

{a} Using a highly concentrated energy beam that provides an energy level of at least 10,000 watts/ground at the interface with the article, the beam can be spread or oscillated to effectively cover a larger control zone and as needed rapidly melts the confined zone of the substrate in response to
Used to generate turbulence in molten metal to promote alloying, 'b} moving a concentrated energy beam relatively rapidly and, when the beam is removed from the confined zone, surrounding dissimilar materials. by providing one or more alloying agents at the interface of the intermediate energy beam and the non-allotropic article to rapidly cool the conduction-heated zone;
using a laser as the energy beam and adjusting the power of the laser beam so that the alloying zone is saturated with the alloying agent and, if necessary, an intermetallic compound is formed that promotes metallic bonding between the alloying zone and the base metal. the level is adjusted with respect to the speed of movement of the beam to provide a beam heating zone of a predetermined depth;'e) the alloying agent is a powder that has been pre-sprayed by plasma, brush etc. and/or has been applied with the appropriate resin onto the base metal; provided as a metallic material or by feeding an alloying wire or foil into the beam adjacent the beam-to-base metal interface so that the base metal is melted simultaneously with the alloying agent;
'Use aluminum or an aluminum alloy as a substrate and use an alloying agent that has an affinity for forming intermetallic compounds with aluminum. The general concept of the invention is that in a treatment zone along the external surface area of an article composed of a non-allotropic metal (of sufficiently high thermal conductivity), improved physical properties can be achieved without adversely affecting the rest of the article. It is to obtain a certain characteristic.

The processing zone is arranged so that it is very small compared to the entire article to reduce costs. This process essentially consists of heating and cooling. Heating consists of focusing a high-energy beam and directing this beam, at a predetermined scanning speed and energy level, measured at the article interface, to a defined zone on the surface of the article, thereby destroying the metal in said zone. melts at a sufficiently fast rate to isolate the remainder of the article from heating effects. Cooling consists of removing the high-energy beam from said zone and proportioning the mass of said article with respect to the beam heating zone, thereby providing a self-imbursing velocity, which results in a fine-grained structure and a supersaturated solid solution. It will be done. Supersaturated solid ports are obtained by diffusing each alloying component into the zone for controlled dilution of the metal or by selecting the alloying base metal with the lowest level of inherent alloying component for supersaturation. . The most notable advantage gained by implementing such a method is the ability to utilize relatively economical, lightweight materials such as aluminum, while isolating the use of expensive materials and reducing physical properties. The ability to limit the improvement to selected wheat surface zones provides an excellent cost/performance ratio.

One important method aspect of using the surface alloying general concept is to provide alloyed surface zones on articles.

Surface alloying is accomplished by rapidly melting selected outer surface zones of the article as well as alloying agents previously or simultaneously placed in said zones. The alloying agent is mixed into the molten base metal by thermal activation due to the action of the beam. Rapid removal of the high-energy beam produces a fine-grained solid port alloy with a distribution of intermetallic compounds due to the self-quenching effect. The creation of such homogeneous surface alloy regions is novel. This is because at least some researchers believed that such highly thermally conductive non-allotropic metals would lose strength as a result of high-energy beam exposure. Some other researchers may have thought that the beam heating zone was not sufficiently confined to allow self-quenching. The beam heating zone provides the required heating and self-quenching rates without compromising
It has been found that a very precisely defined, isolated and controlled space can be created. Reference is made to Figures 1-6 for a detailed description of the preferred manner in which surface alloying is carried out.

{1} The first preliminary step in the method is to select a base material that is sensitive to rapid heating by the high-energy beam, melts easily, and conducts heat well during cooling for self-quenching. Although a wide variety of metallic materials can be used, this embodiment is preferably carried out with a base metal consisting essentially of an aluminum alloy. The base material is at least 0.2&a
It should have a thermal conductivity of 1/unit・sec・℃. Other non-allotropic metals with sufficient thermal conductivity include magnesium, copper, zinc, and titanium. '2' This preferred base metal is surface alloyed by the selection and action of alloying components that have an affinity for the base metal to form solid bodies and intermetallic compounds.

In the case of aluminum or aluminum alloys, the alloying components are copper, nickel, tungsten, molybdenum, zirconium, vanadium, magnesium, zinc, chromium,
It can be selected from the group consisting of cobalt, manganese and titanium. Two or more of such alloy components may be added. Copper is one of the most effective alloying components for hardening aluminum alloys. Nickel prevents aluminum from softening at high temperatures in its alloyed state. Silicon does not form intermetallic compounds, but is useful in aluminum alloys to produce a low silicon core and a highly wear resistant silicon surface. Graphite does not form intermetallic compounds, but is useful as a high temperature solid lubricant in alloyed surface areas. Alloying components for magnesium include zinc, rare earth metals, zirconium, manganese, and aluminum. Alloy ingredients for steel include lead,
zinc, aluminum, tin, iron, nickel, silicon,
These include manganese, beryllium, zirconium, and chromium.
'3} The next step is to apply the alloying components to selected zones of the base metal and expose them to a beam that is deposited or adjacent to said zones.

One way to achieve this is to attach the base metal 1 by a suitable mechanism 12.
1 (see FIG. 1), the mechanism involves spraying powdered alloy metal with a plasma stream. A preferred embodiment is to use a wire consisting of an alloy component and feed this wire into the beam (
(See Figure 6). Yet another method is to mix the resin and powdered alloy components and place this mixture in the path of the beam. Painting methods can also be used if the alloying components are deposited under the influence of the beam. The alloying components to be sprayed by plasma technology can be mixtures of metal powders or can be applied as separate layers. Mixed powders are typically exposed to very high temperatures and jet velocities, but both conditions are not critical to this invention. The depth of the alloy layer should be controlled to obtain a predetermined alloy concentration in the fusion zone of the base metal.

The alloying components (whether added to the base metal or inherent in the base metal) should be subjected to remelting to enrich the base metal fusion zone to form at least a saturated solid solution. In general, surface alloying is primarily aimed at improving one of three physical properties depending on the application of the treated article: wear resistance, fatigue life, and corrosion resistance. In order to provide optimum wear resistance to the processing zone of the article, the alloying components should be added to said zone of molten base metal in a weight ratio of 1:1 to 1:20. This is generally achieved by applying an alloy coating with a thickness equal to or 1/20th the thickness (depth) of the molten base metal. Ratios in this range lead to solidification and the formation of intermetallic compounds in the melt zone, which constitute the primary mechanism of this invention for hardening non-allotropic metals by high energy beam remelting. In order to give the selected surface treatment zone an optimum fatigue life, the ratio should be in the range 1:10 to 1:20, which will dilute the alloy content and prevent the formation of intermetallic compounds. Avoid and promote precipitation hardening or age hardening.

To improve the corrosion resistance of the selected surface treatment zone,
The ratio should be greater than or equal to 2:1. When the base metal is an aluminum alloy such as 390 or 355,
Preferably, substantially pure aluminum is used as the alloying component. Pure aluminum has higher corrosion resistance than the aluminum alloys. A typical apparatus for performing plasma deposition is shown in FIG.

The apparatus uses a plasma gun 15 that includes a gas arc chamber 16 having an exit throat consisting of a straight bore portion 17 and a diverging portion 18 . Gas is introduced into the left side portion of gas chamber 16 from source 31 and an arc is generated across the chamber by arc power source 19. Metal powder and refractory powder are introduced into the gun from a powder feeder 20 and conveyed to a heating tube 21, which is heated by a powder preheating power source 22. The powder is then conveyed to a precise location within the exit throat via a slightly inclined (at 24 with respect to the centerline 25 of the passage) passage 23;
Accurately enters the joint between the straight bore part and the diverging part. From the plasma gun, flow is directed to the target article 26 to be coated. The article to be coated is pressed by a movable support 27;
The powder is deposited over a large area. Article 26 is maintained at a particular electrical potential via arc power supply 28 and subjected to plasma spray particles. The whole article and the plasma jet are vacuum pumped 30
It is housed in a chamber 29 that is evacuated by air. ■
As shown in FIG. 2, the next step is to generate, direct and move a high energy beam to cause melting. A high-energy beam is defined as a radiant energy beam (regardless of its source) that has an average power density of more than 10,000 watts/ground at the interface with the metal to be treated.
column. This step involves generating a high-energy beam 32 of sufficient power, directing the beam to a selected exposure zone 33 of the article, and then moving it along a predetermined path at a specified speed, thereby causing the beam to
0 as well as the base metal 11
The predetermined portion 34 of the adjacent portion is also melted. The beam impacts two zones: a first zone that does not melt and is thermally affected, and a second zone that melts within the first zone. The laser beam initially enters the exposed aluminum surface with some interference from reflection. This disturbance is 'a
}A melt cavity is formed when the heat disintegrates the surface, which allows for the concentration of the light beam, and (b}
Reduced by applying powder alloy coating. The laser beam enters the article at the interface with the high energy, but in the case of an unfocused beam at least some of its intensity is lost due to reflection, diffusion and refraction within the article. However, this is advantageous for controlling shallow beam influence zones. The heating rate of the base metal must be relatively fast so that {a} turbulence is generated in the molten spot pool and {b' the removal of high energy beams promotes rapid cooling.

The absorption properties of the base metal must be controlled to facilitate penetration of the beam into the base metal, thereby promoting rapid heating. This requires the use of a laser beam or an electron beam. Through experiments, 0.15 ribs (0.006
Deposited alloy layer 10 (silicon,
(copper, nickel, and carbon) and adjacent base metals 11 to a depth 36 of 0.025 inches, energy is applied to the article at its interface 37. is about 70,000 watts/ground, and the diameter of the beam spot at the interface is on the two sides (0.
08 inches). This is obtained by means of a laser beam generated by a device 38 (shown in FIGS. 9-11). Defining a suitable high energy laser beam to perform surface alloying is important. The beam generating device is 3.2/sec
It must have a power rating of at least 1 to 1 W to achieve rapid heating and melting at commercial scan rates of (0.005i/sec). At crab force levels below IKW, the beam speed may be reduced to 0.25 objects/minute (0.01 inches/minute), but this speed is not commercially viable. The beam 32 should be centered at a point 40' which is a distance 41 from the plane of the outer surface 37 of the article.
That is, the beam is not centered at the interface with the outer surface of the article, but has a diameter of 39 at that interface, which diameter is actually 0.01 to 0.5 inches. )
is within the range of It is important to control the interaction of the power level of the high energy beam, the scanning speed or relative movement of the beam across the surface 37 of the article, and the spot size of the beam at the interface.

Additionally, as used hereinafter, "control" means correlating the beam interfacial area, scan rate, and beam energy level to achieve the desired melting and cooling rates of the beam influence zone. The energy level at the interface should be at least 10,000 watts/m, and the spot size at the interface should be between 0.5 and 32.
3 pines (0.0008 to 0.05 square inches). Line speed should be in the range of 10-100 inches/minute. Proper control of these parameters results in good temperature distribution in the base metal and good laser surface alloying. The depth 42 of the alloyed surface layer obtained from a single pass is essentially proportional to the energy application level used at a given scan rate. The exact value of the fin force level related to scan speed for a particular surface alloying material or application depends on the alloy coating, the base metal, and the desired alloying surface layer depth. The depth 42 of the alloyed surface layer or beam influence zone is shown in FIG.
The single-pass zone is cross-sectioned by a hemispherical filler 143 and has a solid lacquer of alloyed metal containing intermetallic compounds. The resulting upper surface 44 of the alloyed zone will be higher than the original surface of the article. FIG. 4 shows the profile of a single longitudinal pass.

The entire surface of the article can be covered by {1' by setting multiple buses of non-concentrated east beams, and ■ overlapping the influence zones of each pass, so that the beam influence zones 45 overlap in large numbers as shown in FIG. By causing the lips 46, 47 to appear, an alloyed surface layer can be provided. The spacing and degree of rib overlap can be varied to set up to 4.4 zone depths. It is also possible for each pass to be separated by a wide dimension so that only a pattern of alloyed ribbons or lands appears on the article, giving the required wear resistance to the lands or entire surface of such alloys. I can do it. Additionally, the beam influence zone can be exposed to a focused beam (centered at the interface) and pulsed to balance the melting energy level. A preferred apparatus for generating the laser beam is shown in FIG. 9 and includes a closed C02 gas flow circuit 61 with gas rapidly moved by a blower 62 and heat removed by a heat exchanger 63.

Laser discharge occurs axially along the flow path between electrodes 64 and 65. The laser beam discharge is directed in said axial direction by a fully transmitting mirror 66 and emitted from the laser generator housing by a partially transmitting mirror 67. FIG. 10 shows an apparatus for generating a gas mustard beam by a flow 68 transverse to the electrical discharge between electrodes 69 and 70.

Mirror 71 is partially transmissive. FIG. 11 shows an apparatus that generates a laser beam using an electron beam 72. In FIG.
Sustainer electrodes 73 and 74 are spaced apart in a high vacuum. Electron emitter 75 sends electrons through membrane 76 to the electrode. Mirrors 77, 78 cooperate to collect the laser and transmit the electrons through the partial transmission mirror.
- FIG. 12 shows a device for sending a laser beam 79 from a laser generator 80 to an article 81 to be treated.

The beam is bent by a mirror 82 and collected by a lens 83 into which an auxiliary gas is introduced at 84. Beam orifice 85 controls the beam spot size at the article interface. Laser surface alloying is particularly useful in the following cases:

{a} If the surface of the article requires a special alloy composition for wear resistance, corrosion resistance or heat resistance, (bi If the irregular pattern of the surface requires a special alloy composition, (
c} if the required alloy content cannot be obtained economically in the cast or forged state; {d} if different compositions are required at different locations on the article's surface; [e} if a metallic bond is created between the special surface and the base material. If desired, (f) the heat-affected zone of the base material should be minimized; (g) surface alloying should be achieved with minimal heat input to reduce deformation and damage to adjacent parts due to overheating. , (h) The hardened surface layer should have high hardness even at high temperatures. Yet another apparatus useful for generating high energy beams in the present invention is shown in FIG.

This device is an electron gun that transmits a beam 86 of electrons obtained from a heated filament or an indirectly heated cathode 87. Control electrode 88 adjusts the beam current and the voltage at anode 89, thereby adjusting the velocity of the beam electrons. The product of anode voltage and beam current is the beam power. *The nine east coils independently control the beam spot size, allowing the beam spot size to be adjusted for various voltage values. Deflection coil 91 moves the beam from its neutral axis position and directs it to any point on article 92. Four coils are typically required to deflect the beam in both the x and y directions of the plane of the article. The article and gun share essentially the same vacuum chamber 93. {5) Finally, the beam influence must be removed from the properly molten zone of the article at a sufficiently fast rate, the mass of the article must be balanced to the volume of the molten zone, and the article metal must be , must be selected to have adequate thermal conductivity in order to achieve self-quenching and thereby form small particles or saturated solid solutions of intermetallic compounds.

If the article is a casting and the beam influence zone is in column 3.2 (1
/8 inch) or less, the masses will be properly balanced in almost all cases. Heat Treatment The main purpose of the surface heat treatment according to the present invention is to improve the surface wear resistance or fatigue life of non-allotropic metallic articles with minimal deformation of the article.

This is accomplished by remelting and self-quenching selected zones of the article, either by operation of a non-focusing beam or by vibration of a focusing beam, both without the use of separate alloying agents. The hardening mechanism is crystal and particle refinement. As a result of this, the hardening of the solid hyaline also increases due to the rapid cooling which facilitates the formation of supersaturated solid solutions. As shown in FIG. 7, the heat treatment is performed by using a commercial energy beam 52 having a power level of at least 10,000 watts/ground to remelt typical non-allotropic metals.

The energy is concentrated in the beam, and when it contacts the untreated surface of the article, sufficient energy is present to heat and melt the interfacial zone 54 and the base metal to a greater depth 5, typically about 6
．． Melted up to 4 sides (0.25 inch). Such a beam can be generated by a laser or an electron beam device 53. Quenching occurs when the high energy beam is removed from each beam influence zone by controlling the speed of beam movement and balancing the mass of the article 56 against the beam influence zone 54.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of one initial stage of a preferred method embodiment of the invention. 2 is a schematic cross-sectional view of the next step in the method embodiment of FIG. 1; FIG. FIG. 3 is a schematic cross-sectional view of the product obtained by carrying out the steps of FIGS. 1 and 2. FIG. 4 is a sectional view taken along line 4-4 in FIG. FIG. 5 is a cross-sectional view similar to FIG. 3 showing the result of overlapping multiple passes. FIG. 6 is a diagram similar to FIG. 2 showing another embodiment in which the first and third steps are performed simultaneously. FIG. 7 is a schematic cross-sectional view of an alternative method embodiment of the present invention in which the surface is not alloyed and is directed to heat treatment. FIG. 8 is an enlarged view of a portion of an article treated according to the method of FIG. 9-11 are schematic diagrams of various laser generators useful in the present invention. FIG. 12 is a schematic diagram of a laser concentrator for directing a beam onto an article. 1st
FIG. 3 is a schematic diagram of one type of plasma powder coating equipment that may be used in conjunction with the method of FIGS. 1-3. FIG. 14 is a schematic diagram of one type of electron beam apparatus that may be used in the practice of this invention. 10: Alloy layer, 11: Base metal, 12, 13:
attachment mechanism, 15: plasma gun, 16: gas arc chamber, 19: arc power source, 20: powder feeder, 22:
powder child heat supply source, 26: article, 28: arc power source, 3
0: vacuum pump, 31: gas flow source, 32: beam,
33: exposure zone, 40: focal point, 61: gas flow circuit, 6
2: Blower, 63: Heat exchanger, 64, 65: Electrode, 66
, 67: Mihu, 68: Gas flow, 69, 70: Electrode, 7
1: Mirror, 72: Electron beam, 73, 74: Electrode, 7
6: Film, 77, 78: Mirror, 79: Laser beam, 8
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Claims (1)

Claims: 1. A method of treating selected exposed regions of a non-allotropic metallic article to improve the physical properties of the exposed regions, comprising:
(a) selecting a non-allotropic metal for the article having a thermal conductivity of at least 0.25 cal/cm·sec·°C;
(b) directing a high-energy beam onto an exposed area of the article, heating the article in a zone of beam influence and melting the article to a predetermined depth in a melting zone within the zone of beam influence; at least 10,000 watts/c at the interface with said article
(c) introducing a molten alloy component into the melt zone to mix with the molten metal prior to or simultaneously with directing the high-energy beam at the article, wherein the alloy component is The material is made of a material having an affinity for the non-allotropic metal so as to form a solid solution having an intermetallic compound with the non-allotropic metal and to form precipitate particles, and the introduced alloy component has an affinity for the non-allotropic metal. (d) adjusting the area of the beam interface, the energy level of the beam, and the article; (e) controlling the rate of displacement of the beam along the beam to confine the beam influence zone to a predetermined volume to ensure a predetermined rapid heating rate of the beam influence zone; and (e) reducing the mass of the article to the volume of the beam influence zone. providing a self-hardening rapid cooling rate of the beam-influenced zone when the influence of the beam is removed from the beam-influenced zone in proportion to the molten zone, thereby forming a fine-grained solid solution-hardened structure in at least the molten zone. producing fine precipitate particles. 2. A method as claimed in claim 1, in which the beam interacts with the article to promote turbulent conditions in the molten metal to thoroughly mix the molten alloy components into the molten zone prior to solidification. A method characterized in that the depth of the interface and the melting zone are each controlled. 3. The method according to claim 1, wherein the metal article is made of aluminum or an aluminum alloy. 4. A method according to claim 3, characterized in that the part of the article below the beam influence zone has a thickness at least five times the depth of the beam influence zone. how to. 5. The method of claim 1, wherein the high-energy beam consists of a controlled line similar to visible light, said beam having a focus out of the plane of the surface of said exposed area; Thereby the area of the interface of the beam with the region is at least 0.02 mm^2 (0.000
0.03 square inches). 6. A method according to claim 1, characterized in that the beam is pulsed to achieve an interrupted beam influence zone or to influence a controlled predetermined depth of the melting zone. how to.